An outbreak of varicella among children attending a preschool institution in the North Banat district

Varicella is a highly contagious viral disease that frequently causes outbreaks in preschool settings due to close contact among susceptible children. Although usually mild, it may cause serious complications requiring hospitalization. This study investigated the epidemiological characteristics, transmission dynamics, and clinical outcomes of a varicella outbreak in a preschool institution. An outbreak investigation was conducted among children from two preschool groups affected by varicella in North Banat district (Autonomous Province of Vojvodina, Republic of Serbia). Epidemiological and clinical data, including attack rates, demographic characteristics, vaccination status, and clinical outcomes, were analyzed. The outbreak lasted 61 days (8 October-8 December 2025) and involved 28 cases among 41 children (attack rate 68.3%). Fifteen cases occurred in the older preschool group and 13 in the younger group. The outbreak originated in the older group and subsequently spread to the younger group. The epidemic curve indicated sustained person-to-person transmission. Attack rates were similar between the older and younger groups (65.2% vs. 72.2%, p=0.888). Among affected children, the median age was 6.0 years (IQR, 5.5-6.2) in the older preschool group and 3.6 years (IQR, 3.4-3.8) in the younger preschool group. Among susceptible siblings, the household secondary attack rate was 57.1%. No secondary cases occurred among adult household members. Among unaffected children, a history of prior varicella infection was documented in 88% of children in the older age group and 80% of those in the younger age group. Three children (10.7%) required hospitalization. Two developed varicella cerebellitis 8-9 days after rash onset with neurological manifestations, and one was hospitalized because of prolonged febrile illness and underlying immune deficiency. Follow-up immunological testing identified IgG1 subclass deficiency in two hospitalized children. The mean length of hospital stay was 16 days (range, 10-20 days). The outbreak demonstrated rapid and efficient transmission of varicella virus within a preschool setting, resulting in a high attack rate and clinically significant complications. Neurological complications and immunological abnormalities among hospitalized children highlight the potential severity of varicella and the importance of preventive strategies, including vaccination.